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Title:Microstructure and mechanical properties of a copper-aluminum eutectic
Author(s):Ikeda, Yuki
Advisor(s):Maaß, Robert
Department / Program:Materials Science & Engineerng
Discipline:Materials Science & Engr
Degree Granting Institution:University of Illinois at Urbana-Champaign
Transmission electron microscopy
Scanning transmission electron microscopy
Abstract:The use of intermetallic compound (IMC) for strengthening of alloys is beneficial for high temperature applications because of its hardness and phase stability at high temperature. However, at the same time, its brittle nature often prohibits the application of IMCs at room temperature. For example, Cu-Al IMCs, which are main focus of this work, are known for its excellent conductivity, high corrosion resistance, and light weight but most of them would fracture in a brittle manner. This study aims to overcome this limited plasticity of Cu-Al IMCs by using the idea of plasticity confinement which is found to be effective to activate room temperature plasticity in brittle phases. First, the attempt to fabricate nano-composite was made to obtain a microstructure where a matrix phase was confined by a secondary phase. As a result, CuAl2-CuAl nano-composite was fabricated via diffusion couple method, and the microstructure consisted of brittle phases. Second, nano-indentation was carried out to examine the room temperature plastic behavior of the nano-composite. The composite exhibited room temperature plasticity but its load-displacement curve showed intermittent plastic behavior which was apparently different from those of other Cu-Al IMCs and regular cubic metals. Further statistical analysis and transmission electron microscopy (TEM) revealed that the composite deformed via shear-banding, and the shear-bands were retarded by nano-CuAl phases. Third, microstructure characteristics of the nano-composite were studied by means of TEM and electron diffractions. The nano-CuAl phases were likely to have specific crystallographic orientation relationship with the matrix CuAl2. However, additional real space information, such as atomic arrangement at the interface would be necessary to fully support this conclusion. Finally, a screw dislocation found in the composite was studied. The screw dislocation was accompanied with signatures of cross-slips and stacking faults formation in between two partial dislocations. Analysis by TEM revealed that the cross-slip could not be explained by any slip systems reported so far, which suggests a presence of unknown slip systems in CuAl2. This thesis work is mainly done by experimental methods, and supplemented by TEM image simulations. Thus, as a future suggestion, an aid by means of computational techniques, such as density functional theory would be effective to further support the experimental results described here.
Issue Date:2021-04-28
Rights Information:Copyright 2021 Yuki Ikeda
Date Available in IDEALS:2021-09-17
Date Deposited:2021-05

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